FOS Instrument Science Report CAL/FOS 150


Timing of the FOS in RAPID mode - "Too Rapid RAPID"


J.A. Christensen, W.F. Welsh, I.N. Evans, M. Reinhart, and J.J.E. Hayes

January 8, 1997


ABSTRACT

We present a description of the problems that can occur when using the FOS 
in RAPID mode, including the "too rapid RAPID" phenomenon. At high time 
resolution (i.e. READ-TIMES ~< 10s) the data sampling rate is in general, 
faster than expected. Standard pipeline handling will add an additional 
1/8s uncertainty to the timings due to truncation. However the exposure 
times (thus count rates and fluxes) are unaffected, and the relative 
timings can be accurately reconstructed.

This ISR is written to make the General Observer (GO) aware of these 
problems and to recognise the symptoms in their data.

A technical appendix is included describing in detail die data acquisition 
operations of the FOS. This low-level description is mainly for those 
interested in the fine details of how the FOS acquires and stores data, 
and is includedfor completeness and clarity of technical issues.

A second appendix containing information on a program to determine group 
start times, and a third appendix containing useful equations for 
calculating exposure limes are also included.